Add mbedtls config with nist_kw enabled
Add mbedtls config with nist_kw enabled

This adds a mbedtls config that will enable the simulator to run tests
for the kw based encrypted images.

Signed-off-by: Fabio Utzig <66676b1ceaf93296e098708c09494361103aa635@apache.org>

tamban01/mcuboot,tamban01/mcuboot,runtimeco/mcuboot,runtimeco/mcuboot,ATmobica/mcuboot,runtimeco/mcuboot,ATmobica/mcuboot,runtimeco/mcuboot,utzig/mcuboot,runtimeco/mcuboot,ATmobica/mcuboot,tamban01/mcuboot,utzig/mcuboot,ATmobica/mcuboot,utzig/mcuboot,utzig/mcuboot,ATmobica/mcuboot,utzig/mcuboot,tamban01/mcuboot,tamban01/mcuboot